Rock & Mineral Encyclopedia

Search and identify 1,000+ rocks, minerals, crystals, and gemstones — with properties, formation, colors, hardness, and how to tell them apart.

Tactite

A contact-metasomatic calc-silicate rock, essentially a skarn, formed where intrusions react with carbonate rocks and often host ore.

A calc-silicate rock formed by chemical exchange between magma and carbonate rock, often rich in garnet and economically important ore minerals.

A green ornamental stone, often serpentine-rich marble or verde antique, valued for its rich green color and white veining.

An organic gem formed inside mollusks from layered nacre, prized for its iridescent luster and classic elegance.

Small ironstone concretions from Yowah, Queensland, whose hollow or veined centers hold brilliant precious boulder opal.

A dark green-and-black stromatolite jasper patterned with swirling orbs, formed from fossilized ancient microbial colonies.

Fossilized wood in which the original organic structure has been replaced by opal, sometimes showing precious play-of-color.

An iron-rich sedimentary rock, often heavy and rusty-weathering, historically mined as a major source of iron ore.